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HK: Physik der Hadronen und Kerne

HK 3: Theorie I

HK 3.6: Talk

Monday, March 19, 2001, 18:15–18:30, B

Ordinary and Radiative Muon Capture on the Proton — •T.R. Hemmert², V. Bernard¹ und U.-G. Meißner³ — ¹U. L. Pasteur, LPT, Strasbourg, France — ²Physik-Department T39, TU München — ³FZ-Jülich, IKP(Th), Jülich, Germany

We calculate [1] ordinary and radiative muon capture on the proton in a chiral effective field theory of pions, nucleons and delta isobars as explicit degrees of freedom. Preceding calculations [2] using standard heavy baryon chiral perturbation theory (chpt)—which only employs pion and nucleon degrees of freedom—were not able to reproduce the photon spectrum in the pioneering experiment of radiative muon capture on the proton from TRIUMF [3]. For the past few years it has been speculated that the discrepancy between theory and experiment might be due to Delta(1232) related effects, which are only included via higher order contact interactions in the chpt approach. In this report we demonstrate that this speculation does not hold true. We show that contrary to expectations from naive dimensional analysis isobar effects on the photon spectrum and the total rate in radiative muon capture are of the order of a few percent and present some new ideas that might be at the bottom of the still unresolved discrepancy between theory and experiment in radiative muon capture. Finally we show that the procedure employed by the TRIUMF group to extract information from their radiative muon capture experiment on the pseudoscalar coupling constant g_p is fundamentally flawed and even leads to inconsistencies with ordinary muon capture data.

[1] V. Bernard, T.R. Hemmert and U.G. Meißner, [nucl-th/0001052], Nucl. Phys. A in press

[2] e.g. S.I. Ando and D.P. Min, Phys. Lett. B417, 177 (1998)

[3] G. Jonkmans et al., Phys. Rev. Lett. 77, 4512 (1996)